STSS DEMO 2 (USA 209) is part of a $1.5 billion project known as STSS Demo. The satellites will be used together with STSS DEMO 1 by the U.S. Missile Defense Agency to test the "birth to death" tracking of missiles from launch to re-entry. The two craft, weighing nearly 5,000 pounds [2,268 kg] at launch and each having pairs of power-generating solar wings, are equipped with infrared and visible sensors to spot missile launches, track the vehicles through space and observe the entry back into the atmosphere. By working together from separate vantage points in low-Earth orbit, their imagery will combine to provide 3-D tracking of objects.